Effect of deep cryogenic cycling treatment on the microstructure and mechanical properties of Ti-based bulk metallic glass

•The amorphous nature and the thermostability of the Ti33Zr30Cu9Ni5.5Be22.5 BMG were almost unaffected by the DCT.•The DCT30 specimen exhibited a more prominent rejuvenation behavior manifested by a higher relaxation enthalpy.•The room-temperature plasticity of DCT30 specimen increased from 1.4% of...

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Bibliographic Details
Published in:	Journal of alloys and compounds 2021-12, Vol.887, p.161386, Article 161386
Main Authors:	Lv, J.W., Wang, F.L., Yin, D.W., Zhang, S., Cai, Z.Q., Shi, Z.L., Ma, M.Z., Zhang, X.Y.
Format:	Article
Language:	eng
Subjects:	Amorphous materials Bulk metallic glass Compressive property Cryogenic treatment Deep cryogenic cycle Densification Edge dislocations Enthalpy Free energy Heat of formation Mechanical properties Metallic glasses Microstructure Nanoindentation Plastic properties Relaxation enthalpy Room temperature Shear bands Shear transformation zone Titanium
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Summary:	•The amorphous nature and the thermostability of the Ti33Zr30Cu9Ni5.5Be22.5 BMG were almost unaffected by the DCT.•The DCT30 specimen exhibited a more prominent rejuvenation behavior manifested by a higher relaxation enthalpy.•The room-temperature plasticity of DCT30 specimen increased from 1.4% of the as-cast state to 7.8%.•The DCT30 specimen obtained the lowest average stress drop (15.9 MPa) and shear band formation energy (342.8 J/m2).•The DCT30 specimen possesses the larger volume and size of STZs. This study investigates the effect of deep cryogenic cycle treatment (DCT) on the microstructure and mechanical behaviors of Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG). The results revealed that after the DCT, the relaxation enthalpy increased, whereas the Ti33Zr30Cu9Ni5.5Be22.5 BMG still maintained a complete amorphous nature. As the cycle numbers increased, the room-temperature plasticity of the Ti33Zr30Cu9Ni5.5Be22.5 BMG represented a tendency to increase first and then decrease. When the cycle numbers increased to 30, the Ti33Zr30Cu9Ni5.5Be22.5 BMG obtained the maximum compressive plasticity of 7.8%, which is 5.6 times that of the as-cast specimen, accompanied by a higher strength. Moreover, the nanoindentation results demonstrated that the Ti33Zr30Cu9Ni5.5Be22.5 BMG that underwent the DCT possessed a larger pop-in size, a lower initial pop-in force and a lower hardness. The shear transformation zone (STZ) theory was employed to elucidate the plasticising mechanism induced by the DCT for the Ti33Zr30Cu9Ni5.5Be22.5 BMG. The larger STZ volumes and the lower shear band formation energy induced through the DCT promoted the densification of multiple shear bands, which is the principal reason for the excellent plasticity after the DCT.
ISSN:	0925-8388 1873-4669